SEGREGATION OF TYPE-1 CYTOKINE PRODUCTION IN HUMAN PERIPHERAL-BLOOD LYMPHOCYTES - PHENOTYPIC DIFFERENCES BETWEEN IFN-GAMMA, AND IL-2-PRODUCING CELLS IN THE CD8(-CELL SUBSET() T)

T cell clones are classified as type 0, I or 2 depending on the lympho kines they produce. However, it has remained unclear whether single ce lls of a given type produce one or several cytokine species. Flow cyto metric analysis of peripheral blood lymphocytes (PBL) obtained from 20 healthy donors for the production of the type I cytokines IFN-gamma a nd IL-2 revealed very few cells that co-expressed both cytokines indep endently of the mitogenic stimulus used for PBL activation. Similarly, kinetic studies of cytokine synthesis indicated a low percentage of I FN-gamma/IL-2 double-positive T cells at all time points. Reverse tran scription-PCR analysis of sorted IL-2- and IFN-gamma-positive T cells showed the presence of IL-2- or IFN-gamma-specific mRNA only in those cells expressing the corresponding cytokine. This segregation of the t wo type I cytokines was lost in long-term cultured T cells and in T ce ll clones. A high percentage of cells expressing only IL-2 or IFN-gamm a was observed even when the production of these cytokines was evaluat ed on CD4(+) and CD8(+) subsets. Moreover, in some healthy individuals , IFN-gamma and IL-2 production by CD8(+) T cells was related to CD8() expression levels and cell size, i.e. IL-2-expressing cells were gen erally smaller with more intense CD8(+) staining as compared with IFN- gamma-producing T cells. These data indicate that activated T lymphocy tes are strongly committed in vivo to produce IFN-gamma or IL-2 and em phasizes the independent regulation of the two cytokine genes.